Pure Live Seed (PLS) Calculator
Convert bulk seed weight to pure live seed — and find the bulk pounds you need to hit a PLS target.
What this does
Enter bulk seed weight with the purity and germination percentages from the seed tag. The calculator returns the pure live seed (PLS) you actually have — or, in reverse, the bulk pounds needed to hit a PLS target — so you can compare seed lots fairly and buy the right amount of native or wildflower seed.
Purity × germination
bulk_needed = PLS_target ÷ (purity% × germination%)
%PLS = purity% × germination% (seed-tag quality)
Pure live seed strips out dead seed and inert matter — chaff, sand, weed seed — so a pound of one lot compares fairly to a pound of another. It’s standard for native grasses and wildflowers, where purity and germination vary widely.
Both numbers come off the seed tag: purity (the share of the bag that’s your seed) and germination (the share of that seed that will sprout). Multiply them for the %PLS, then apply it to weight.
Worked example: 10 lb of bulk seed at 95% purity and 85% germination is 10 × 0.95 × 0.85 = 8.1 lb of pure live seed. To sow 8 lb PLS you’d need 8 ÷ (0.95 × 0.85) ≈ 9.9 lb of bulk seed.
Method & data pinned to: Seed-testing standard (AOSA / extension seed labs) — v2026-06.
Run the numbers
The interactive Pls Calculator loads here.
Until then, the formula above gives the same result by hand.
Step by step
- 1. Read purity and germination % off the seed tag.
- 2. Enter your bulk seed weight — or switch to target mode and enter the PLS you need.
- 3. Read your pure live seed, or the bulk pounds required.
- 4. Use the PLS figure to compare lots and price per live pound.
- 5. Feed the bulk weight into the Seed Cost Calculator.
Getting an accurate answer
PLS matters most for native grasses, wildflower mixes, and anything sold by bulk weight, where purity and germination swing a lot between lots.
For clean, high-germination lawn seed — most clover and fescue — bulk and PLS are close, but the tag still tells you exactly.
Data source & assumptions
Pinned to Seed-testing standard (AOSA / extension seed labs) (v2026-06). Assumptions:
- Purity and germination taken from the seed tag.
- %PLS = purity × germination.
- Total germination per tag (hard seed counted as labelled).
- Excludes seeding rate — pair with the Seed Coverage Calculator.
Common questions
What is pure live seed?
The weight of seed in a bag that will actually grow — bulk weight adjusted for purity and germination. It lets you compare lots fairly.
Where do I find purity and germination?
On the seed tag or analysis label required on every bag. Look for “pure seed %” and “germination %.”
Why do native seeds need PLS?
Native grass and wildflower lots vary a lot in cleanliness and viability, so they’re sold and sown by PLS to keep rates honest.
Is high-germination lawn seed different?
Only in degree — clean clover and fescue have high purity and germination, so bulk and PLS are close. The tag still gives you the exact figures.